Method of manufacturing solar cell

ABSTRACT

A method of manufacturing a solar cell, the method includes forming a protective film over a semiconductor substrate, the semiconductor substrate including a base area of a first conductive type and formed of crystalline silicon, wherein the forming of the protective film includes a heat treatment process performed at a heat treatment temperature of approximately 600 degrees Celsius or more under a gas atmosphere including nitrogen, and wherein the heat treatment process includes: a main section, during which the heat treatment temperature is maintained, a temperature increase section before the main section, during which an increase in temperature occurs from an introduction temperature to the heat treatment temperature, and a temperature reduction section after the main section, during which a decrease in temperature occurs from the heat treatment temperature to a discharge temperature.

CROSS-REFERENCE TO RELATED APPLICATIONS

This Application is a Continuation of co-pending U.S. patent applicationSer. No. 15/178,274 filed on Jun. 9, 2016, which claims the benefitunder 35 U.S.C. § 119(a) to Korean Patent Application Nos.10-2016-0053932 filed on May 2, 2016 and 10-2015-0082111 filed on Jun.10, 2015, all of which are hereby expressly incorporated by referenceinto the present application.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a method of manufacturing a solar cell,and more particularly to a method of manufacturing a solar cell having aprotective film formed over a semiconductor substrate or over aconductive area.

Discussion of the Related Art

Recently, due to depletion of existing energy resources, such as oil andcoal, interest in alternative sources of energy to replace the existingenergy resources is increasing. Most of all, solar cells are popularnext generation cells to convert sunlight into electrical energy.

Solar cells may be manufactured by forming various layers and electrodesbased on some design. The efficiency of solar cells may be determined bythe design of the various layers and electrodes. In order for solarcells to be commercialized, the problem of low efficiency needs to beovercome, and thus, there is a demand to design the various layers andelectrodes so as to maximize the efficiency of solar cells.

In one example, solar cells are provided with various protective films,in order to realize the passivation, physical protection, and electricalinsulation of a semiconductor substrate or a semiconductor layer. Theseprotective films may be formed by, for example, thermal oxidation ordeposition. A protective film formed by thermal oxidation may make itdifficult to precisely control the thickness thereof and to achieveexcellent film properties. In addition, deposition is performed under anatmosphere including source gas, which contains elements forconstituting a protective film, and, as needed, carrier gas. However,the protective film, formed using only basic gas, such as a source gasand carrier gas, may have a high interface trap density and may notprovide good passivation for a semiconductor substrate or asemiconductor layer. Therefore, there is demand for a method ofmanufacturing a protective film having good properties.

SUMMARY OF THE INVENTION

Therefore, the embodiments of the present invention have been made inview of the above problems, and it is an object of the present inventionto provide a method of manufacturing a solar cell, which enables themanufacture of a solar cell having good efficiency through the formationof a protective film having good properties.

In accordance with an aspect of the present invention, the above andother objects can be accomplished by the provision of a method ofmanufacturing a solar cell including forming a protective film using aninsulation film over a semiconductor substrate, the semiconductorsubstrate including a base area of a first conductive type and formed ofcrystalline silicon. The forming of the protective film includes a heattreatment process performed at a heat treatment temperature of 600degrees Celsius or more under a gas atmosphere including halogen gas,which has a halogen element.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and other advantages of thepresent invention will be more clearly understood from the followingdetailed description taken in conjunction with the accompanyingdrawings, in which:

FIG. 1 is a sectional view illustrating one example of a solar cellmanufactured by a method of manufacturing the solar cell in accordancewith one embodiment of the present invention;

FIG. 2 is a partial rear plan view of the solar cell illustrated in FIG.1;

FIGS. 3A to 3F are sectional views illustrating the method ofmanufacturing the solar cell in accordance with one embodiment of thepresent invention;

FIG. 4 is a view illustrating one example of a heat treatment device,which may perform a heat treatment process in the method ofmanufacturing the solar cell in accordance with one embodiment of thepresent invention;

FIG. 5 is a view illustrating the temperature cycle of the heattreatment process in the method of manufacturing the solar cell inaccordance with one embodiment of the present invention;

FIGS. 6A and 6B are sectional views illustrating an operation of forminga control passivation layer in the method of manufacturing the solarcell in accordance with one embodiment of the present invention;

FIG. 7 is a sectional view illustrating another example of the solarcell manufactured by the method of manufacturing the solar cell inaccordance with one embodiment of the present invention;

FIG. 8 is a schematic plan view of the solar cell illustrated in FIG. 7;

FIGS. 9A to 9D are sectional views illustrating the method ofmanufacturing the solar cell in accordance with another embodiment ofthe present invention;

FIGS. 10A to 10D are sectional views illustrating the method ofmanufacturing the solar cell in accordance with a further embodiment ofthe present invention;

FIG. 11 is a photoluminescence (PL) photograph of the solar cell inaccordance with Experimental Example 1;

FIG. 12 is a PL photograph of the solar cell in accordance withComparative Example 1;

FIG. 13 is a PL photograph of the solar cell in accordance withComparative Example 2;

FIG. 14 is a graph illustrating results of measuring the impliedopen-circuit voltages of the solar cells in accordance with ExperimentalExample 1 and Comparative Example 1; and

FIG. 15 is a graph illustrating results of measuring the impliedopen-circuit voltages of the solar cells in accordance with ExperimentalExamples 1 and 2 and Comparative Example 1, after performing additionalheat treatment at the temperature of 900 degrees Celsius.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Reference will now be made in detail to the example embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings. However, it will be understood that the present inventionshould not be limited to the embodiments and may be modified in variousways.

In the drawings, to clearly and briefly explain the present invention,illustration of elements having no connection with the description isomitted, and the same or extremely similar elements are designated bythe same reference numerals throughout the specification. In addition,in the drawings, for a more clear explanation, the dimensions ofelements, such as thickness, width, and the like, are exaggerated orreduced, and thus the thickness, width, and the like of the embodimentsof the present invention are not limited to the illustration of thedrawings.

In addition, in the entire specification, when an element is referred toas “including” another element, the element should not be understood asexcluding other elements so long as there is no special conflictingdescription, and the element may include at least one other element. Inaddition, it will be understood that, when an element such as a layer,film, region or substrate is referred to as being “over” anotherelement, it can be directly over the other element or interveningelements may also be present. On the other hand, when an element such asa layer, film, region or substrate is referred to as being “directlyover” another element, this means that there are no intervening elementstherebetween.

Hereinafter, a method of manufacturing a solar cell in accordance withthe embodiments of the present invention will be described withreference to the accompanying drawings. One example of a solar cell,manufactured by the method of manufacturing the solar cell in accordancewith the embodiments of the present invention, will first be described,and thereafter, the method of manufacturing the solar cell in accordancewith the embodiments of the present invention will be described.

FIG. 1 is a sectional view illustrating one example of a solar cell,manufactured by a method of manufacturing the solar cell, in accordancewith an embodiment of the present invention, and FIG. 2 is a partialrear plan view of the solar cell illustrated in FIG. 1.

With reference to FIGS. 1 and 2, the solar cell, designated by referencenumeral 100, in accordance with the present embodiment includes asemiconductor substrate 10 including a base area 110, conductive areas32 and 34 formed on or over the semiconductor substrate 10, electrodes42 and 44 connected to the conductive areas 32 and 34, and a protectivefilm formed over (e.g. in contact with) the semiconductor substrate 10.The present embodiment illustrates that a control passivation layer 20,disposed over the semiconductor substrate 10, constitutes theaforementioned protective film, and a semiconductor layer 30, whichincludes the conductive areas 32 and 34, is disposed over the controlpassivation layer 20. Here, the semiconductor layer 30 includes a firstconductive area 32 of a first conductive type and a second conductivearea 34 of a second conductive type, and an intrinsic barrier area 36may be interposed between the first conductive area 32 and the secondconductive area 34. In addition, the electrodes 42 and 44 may include afirst electrode 42 connected to the first conductive area 32 and asecond electrode 44 connected to the second conductive area 34. Inaddition, the solar cell 100 may further include additional protectivefilms, such as a front passivation film 24, an anti-reflection film 26,and a back passivation film 40. Here, the protective films may beinsulation films for protecting the semiconductor substrate 10 or theconductive areas 32 and 34. The aforementioned constituent elements willbe described below in more detail.

The semiconductor substrate 10 may include the base area 110, whichincludes a second conductive dopant at a relatively low dopingconcentration, thus being of the second conductive type. The base area110 may be formed of crystalline semiconductors including the secondconductive dopant. In one example, the base area 110 may be formed ofmonocrystalline or polycrystalline semiconductors (e.g. monocrystallineor polycrystalline silicon) including the second conductive dopant. Moreparticularly, the base area 110 may be formed of monocrystallinesemiconductors including the second conductive dopant (e.g. amonocrystalline semiconductor wafer, and for example, a semiconductorsilicon wafer). The use of the base area 110 or the semiconductorsubstrate 10 having high crystallinity and thus low defects ensuresexcellent electrical properties.

The second conductive type may be a p-type or an n-type. In one example,when the base area 110 is of an n-type, the p-type first conductive area32 may be widely formed in order to increase a photoelectric conversionarea. Both the base area 110 and the p-type first conductive area 32form a junction (e.g. a pn junction) with the control passivation layer20 interposed therebetween for forming carriers via photoelectricconversion. In addition, in this instance, the first conductive area 32having a wide area may effectively collect holes, which move relativelyslowly, thereby contributing to an increase in photoelectric conversionefficiency. However, the embodiment of the present invention is notlimited thereto.

In addition, the semiconductor substrate 10 may include a front fieldarea (or a field area) 130 disposed on the front surface of thesemiconductor substrate 10. The front field area 130 may be of the sameconductive type as the conductive type of the base area 110, but mayhave a higher doping concentration than the base area 110. Therefore,the front field area 30 may constitute a conductive area or a dopantarea.

The present embodiment illustrates the configuration in which the frontfield area 130 is a doped area formed by doping the semiconductorsubstrate 10 with the second conductive dopant at a relatively highdoping concentration. As such, the front field area 130 includescrystalline (monocrystalline or polycrystalline) semiconductors of thesecond conductive type so as to constitute a portion of thesemiconductor substrate 10. In one example, the front field area 130 mayconstitute a portion of a monocrystalline semiconductor substrate (e.g.a monocrystalline silicon wafer substrate) of the second conductivetype. At this time, the doping concentration of the front field area 130may be lower than the doping concentration of the second conductive area34, which is of the same second conductive type as the conductive typeof the front field area 130.

However, the embodiment of the present invention is not limited thereto.Thus, the front field area 130 may be formed by doping a semiconductorlayer (e.g. an amorphous semiconductor layer, a microcrystallinesemiconductor layer, or a polycrystalline semiconductor layer), separatefrom the semiconductor substrate 10, with the second conductive dopant.Alternatively, the front field area 130 may be an area, which servessimilar to an area doped with a fixed charge of a layer (e.g. the frontpassivation film 24 and/or the anti-reflection film 26), which is formedadjacent to the semiconductor substrate 10. For example, when the basearea 110 is of an n-type, the front passivation film 24 may be formed ofan oxide having a negative fixed charge (e.g. an aluminum oxide) so asto form an inversion layer on the surface of the base area 110. Thereby,the inversion layer may be used as a field area. In this instance, thesemiconductor substrate 10 may include only the base area 110 without aseparate doped area, which may minimize defects of the semiconductorsubstrate 10. Various other configurations of the front field area 130may be formed using various other methods.

In the present embodiment, the front surface of the semiconductorsubstrate 10 may be subjected to texturing so that the front surface isprovided with protrusions having, for example, a pyramidal shape. Theresulting texture formed on the semiconductor substrate 10 may have agiven shape (e.g. a pyramidal shape) having an outer surface formed on aspecific crystal face (e.g. (111) face) of semiconductors. When theroughness of, for example, the front surface of the semiconductorsubstrate 10 is increased by the protrusions formed on the front surfacevia texturing, it is possible to reduce the reflectance of lightintroduced through the front surface of the semiconductor substrate 10.Accordingly, the quantity of light, which reaches the pn junction formedby the base area 110 and the first conductive area 32, may be increased,which may minimize the loss of light.

In addition, the back surface of the semiconductor substrate 10 may beformed via, for example, mirror surface grinding, and thus may be arelatively smooth flat surface, which has a lower surface roughness thanthat of the front surface. In the instance where both the first andsecond conductive areas 32 and 34 are formed on the back surface of thesemiconductor substrate 10 as in the present embodiment, the propertiesof the solar cell 100 may be greatly changed according to the propertiesof the back surface of the semiconductor substrate 10. Therefore, theback surface of the semiconductor substrate 10 may have no protrusionformed via texturing in order to improve passivation, which mayconsequently improve the properties of the solar cell 100. However, theembodiment of the present invention is not limited thereto. In someinstances, the back surface of the semiconductor substrate 10 may beprovided with protrusions via texturing. Various other alterations arepossible.

The control passivation layer 20, which is a protective film formed overthe semiconductor substrate 10, may be formed on the back surface of thesemiconductor substrate 10. In one example, the control passivationlayer 20 may come into contact with the back surface of thesemiconductor substrate 10, which may result in the simplifiedconfiguration. In addition, the control passivation layer 20 may beformed on the entire back surface of the semiconductor substrate 10, soas to be formed via a simplified process without additional patterning.However, the embodiment of the present invention is not limited thereto,and various alterations in terms of, for example, the shape of thecontrol passivation layer 20 are possible.

The control passivation layer 20 may serve as a diffusion barrier forpreventing dopants in the conductive areas 32 and 34 from being diffusedto the semiconductor substrate 10. The control passivation layer 20 mayinclude various materials to enable the passage of a plurality ofcarriers therethrough. In one example, the control passivation layer 20may include an oxide or a nitride. More particularly, the controlpassivation layer 20 may be a silicon oxide layer including a siliconoxide. This is because the silicon oxide layer has good passivation andensures easy carrier movement. The control passivation layer 20 may be alayer formed by wet chemical oxidation and/or thermal oxidation underspecific conditions. This will be described later in more detail.

At this time, the control passivation layer 20 may be thinner than theback passivation film 40. In one example, the thickness of the controlpassivation layer 20 may be 5 nm or less (for example, 2 nm or less,e.g. within a range from 1 nm to 2 nm). When the thickness of thecontrol passivation layer 20 exceeds 5 nm, smooth carrier movement doesnot occur, which prevents the solar cell 100 from operating. In order toensure smoother carrier movement, the thickness of the controlpassivation layer 20 may be 2 nm or less. The control passivation layer20, which has a small thickness of 2 nm or less as described above, mayensure the smooth transfer of carriers, which may enhance the fillfactor (FF) of the solar cell 100. When the thickness of the controlpassivation layer 20 is below 1 nm, it may be difficult to form thecontrol passivation layer 20 having desired qualities. However, theembodiment of the present invention is not limited thereto, and thethickness of the control passivation layer 20 may have any of variousvalues.

The semiconductor layer 30, which includes the conductive areas 32 and34, may be disposed over the control passivation layer 20. In oneexample, the semiconductor layer 30 may come into contact with thecontrol passivation layer 20, which may simplify the entireconfiguration. However, the embodiment of the present invention is notlimited thereto.

In the present embodiment, the semiconductor layer 30 may include thefirst conductive area 32, which includes a first conductive dopant andexhibits a first conductive type, and the second conductive area 34,which includes a second conductive dopant and exhibits a secondconductive type. The first conductive area 32 and the second conductivearea 34 may be located in the same plane over the control passivationlayer 20. That is, there may be no layer interposed between the firstconductive area 32 and the control passivation layer 20 and between thesecond conductive area 34 and the control passivation layer 20.Alternatively, when another layer is interposed between the first andsecond conductive areas 32 and 34 and the control passivation layer 20,the interposed layer may have the same stacking configuration betweenthe first conductive area 32 and the control passivation layer 20 andbetween the second conductive area 34 and the control passivation layer20. In addition, the barrier area 36 may be located between the firstconductive area 32 and the second conductive area 34 in the same planeas the conductive areas 32 and 34.

The first conductive area 32 is an emitter area, which forms a pnjunction (or a pn tunnel junction) with the base area 110 with thecontrol passivation layer 20 interposed therebetween, so as to generatecarriers via photoelectric conversion.

At this time, the first conductive area 32 may include a semiconductor(e.g. silicon) including the first conductive dopant, which is contraryto that of the base area 110. In the present embodiment, the firstconductive area 32 is a semiconductor layer, which is separately formedover the semiconductor substrate 10 (more particularly, over the controlpassivation layer 20) and which is doped with a first conductive dopant.As such, the first conductive area 32 may be a semiconductor layer,which has a different crystalline structure from that of thesemiconductor substrate 10 so as to be easily formed on thesemiconductor substrate 10. For example, the first conductive area 32may be formed by doping, for example, an amorphous semiconductor, amicrocrystalline semiconductor, or a polycrystalline semiconductor (e.g.amorphous silicon, microcrystalline silicon, or polycrystallinesilicon), which may be easily fabricated via various methods such as,for example, deposition, with the first conductive dopant. The firstconductive dopant may be introduced to the semiconductor layer while thesemiconductor layer is formed, or may be introduced to the semiconductorlayer after the semiconductor layer is formed, via any of various dopingmethods, such as thermal diffusion or ion implantation.

At this time, the first conductive area 32 may include the firstconductive dopant, which may exhibit a conductive type contrary to thatof the base area 110. That is, when the first conductive dopant is ap-type dopant, it may use a group III element, such as boron (B),aluminum (Al), gallium (Ga), or indium (In). When the first conductivedopant is an n-type dopant, it may use a group V element, such asphosphorus (P), arsenic (As), bismuth (Bi), or antimony (Sb). In oneexample, the first conductive dopant may be boron (B), which is of ap-type.

The second conductive area 34 serves as a back field area, which forms aback field to prevent the loss of carriers from the surface of thesemiconductor substrate 10 (for example, the back surface of thesemiconductor substrate 10) due to recombination.

At this time, the second conductive area 34 may include a semiconductor(e.g. silicon), which includes the same second conductive dopant as theconductive type of the base area 110. In the present embodiment, thesecond conductive area 34 is a semiconductor layer, which is separatelyformed over the semiconductor substrate 10 (more clearly, over thecontrol passivation layer 20) and which is doped with the secondconductive dopant. As such, the second conductive area 34 may be asemiconductor layer having a crystalline structure, which is differentfrom that of the semiconductor substrate 10, so as to be easily formedon the semiconductor substrate 10. For example, the second conductivearea 34 may be formed by doping, for example, an amorphoussemiconductor, a microcrystalline semiconductor, or a polycrystallinesemiconductor (e.g. amorphous silicon, microcrystalline silicon, orpolycrystalline silicon), which may be easily fabricated via variousmethods such as, for example, deposition, with the second conductivedopant. The second conductive dopant may be introduced to thesemiconductor layer while the semiconductor layer is formed, or may beintroduced to the semiconductor layer after the semiconductor layer isformed, via any of various doping methods, such as thermal diffusion orion implantation.

At this time, the second conductive area 34 may include the secondconductive dopant, which may exhibit the same conductive type as theconductive type of the base area 110. That is, when the secondconductive dopant is an n-type dopant, it may use a group V element,such as phosphorus (P), arsenic (As), bismuth (Bi), or antimony (Sb).When the second conductive dopant is an n-type dopant, it may use agroup III element, such as boron (B), aluminum (Al), gallium (ga), orindium (In). In one example, the second conductive dopant may bephosphorus (P), which is of an n-type.

In addition, the barrier area 36 is located between the first conductivearea 32 and the second conductive area 34 so that the first conductivearea 32 and the second conductive area 34 are spaced apart from eachother. When the first conductive area 32 and the second conductive area34 come into contact with each other, shunts occur, undesirably causingdeterioration in the performance of the solar cell 100. However, in thepresent embodiment, it is possible to prevent unnecessary shunts bypositioning the barrier area 36 between the first conductive area 32 andthe second conductive area 34.

The barrier area 36 may include any of various materials, which may belocated between the first conductive area 32 and the second conductivearea 34 so as to substantially insulate the conductive areas 32 and 34from each other. That is, the barrier area 36 may be formed of anundoped insulation material (e.g. an oxide or a nitride). Alternatively,the barrier area 36 may include an intrinsic semiconductor. At thistime, the first conductive area 32, the second conductive area 34 andthe barrier area 36 may be formed of the same semiconductor (e.g.amorphous silicon, microcrystalline silicon or polycrystalline silicon),which is continuously formed such that side surfaces of the three areas32, 34 and 36 come into contact with one another. The barrier area 36may include an i-type (intrinsic) semiconductor material, whichsubstantially includes no dopant. In one example, after a semiconductorlayer including a semiconductor material is formed, a portion of thesemiconductor layer is doped with the first conductive dopant so as toform the first conductive area 32 and another portion of thesemiconductor layer is doped with the second conductive dopant so as toform the second conductive area 34, whereby the remaining area on whichthe first conductive area 32 and the second conductive area 34 are notformed may be the barrier area 36. In this way, the manufacture of thefirst conductive area 32, the second conductive area 34, and the barrierarea 36 may be simplified.

However, the embodiment of the present invention is not limited thereto.Thus, when the barrier area 36 is formed separately from the firstconductive area 32 and the second conductive area 34, the thickness ofthe barrier area 36 may differ from those of the first conductive area32 and the second conductive area 34. In one example, in order to moreeffectively prevent short-circuit between the first conductive area 32and the second conductive area 34, the barrier area 36 may be thickerthan the first conductive area 32 and the second conductive area 34.Alternatively, in order to reduce the amount of raw materials requiredto form the barrier area 36, the barrier area 36 may be thinner than thefirst conductive area 32 and the second conductive area 34. Of course,various other alterations are possible. In addition, the basicconstituent material of the barrier area 36 may differ from those of thefirst conductive area 32 and the second conductive area 34.

In addition, the present embodiment illustrates the configuration inwhich the barrier area 36 causes the first conductive area 32 and thesecond conductive area 34 to be wholly spaced apart from each other.However, the embodiment of the present invention is not limited thereto.Accordingly, the barrier area 36 may be formed to cause the firstconductive area 32 and the second conductive area 34 to be spaced apartfrom each other only along a portion of the boundary therebetween.Thereby, the conductive areas 32 and 34 may come into contact with eachother along the remaining portion of the boundary between the firstconductive area 32 and the second conductive area 34.

Here, the first conductive area 32, which is of a different conductivetype from the conductive type of the base area 110, may be wider thanthe second conductive area 34, which is of the same conductive type asthe conductive type of the base area 110. As such, the pn junction,which is formed through the control passivation layer 20 between thebase area 110 and the first conductive area 32, may have an increasedwidth. At this time, when the conductive type of the base area 110 andthe second conductive area 34 is an n-type and the conductive type ofthe first conductive area 32 is a p-type, the wide first conductive area32 may effectively collect holes, which move relatively slowly. The planconfiguration of the first conductive area 32, the second conductivearea 34, and the barrier area 36 will be described below in more detailwith reference to FIG. 2.

The back passivation film 40 may be formed over the first and secondconductive areas 32 and 34 and the barrier area 36 on the back surfaceof the semiconductor substrate 10. In one example, the back passivationfilm 40 may be formed so as to come into contact with the first andsecond conductive areas 32 and 34 and the barrier area 36, thus having asimplified configuration. However, the embodiment of the presentinvention is not limited thereto.

The back passivation film 40 has openings 402 and 404 for electricallyconnecting the conductive areas 32 and 34 and the electrodes 42 and 44to each other. The openings 402 and 404 include a first opening 402 forconnecting the first conductive area 32 and the first electrode 42 toeach other, and a second opening 404 for connecting the secondconductive area 34 and the second electrode 44 to each other. As such,the back passivation film 40 serves to prevent the first conductive area32 and the second conductive area 34 from being connected to theincorrect electrode (i.e. the second electrode 44 in the instance of thefirst conductive area 32 and the first electrode 42 in the instance ofthe second conductive area 34). In addition, the back passivation film40 may be used for the passivation of the first and second conductiveareas 32 and 34 and/or the barrier area 36.

The back passivation film 40 may take the form of a single layer ormultiple layers including a silicon oxide, a silicon nitride, a siliconoxide nitride, a silicon carbide, amorphous silicon, or the like.

The back passivation film 40 may be disposed over a portion of thesemiconductor layer 30 on which the electrodes 42 and 44 are notlocated. The back passivation film 40 may be thicker than the controlpassivation layer 20. As such, the insulation and passivation propertiesof the back passivation film 40 may be improved. Various otheralterations are possible.

In one example, in the present embodiment, the front passivation film 24and/or the anti-reflection film 26 and the back passivation film 40 mayinclude no dopant in order to achieve, for example, excellent insulationand passivation properties.

The electrodes 42 and 44, arranged on the back surface of thesemiconductor substrate 10, include the first electrode 42 electricallyand physically connected to the first conductive area 32 and the secondelectrode 44 electrically and physically connected to the secondconductive area 34.

The first and second electrodes 42 and 44 may include various metalmaterials. In addition, the first and second electrodes 42 and 44 mayhave various plan shapes required in order to be connected respectivelyto the first conductive area 32 and the second conductive area 34without being electrically connected to each other so as to collectcarriers and transmit the same to the outside. That is, the embodimentof the present invention is not limited as to the plan shape of thefirst and second electrodes 42 and 44.

Hereinafter, one example of the plan shape of the first conductive area32, the second conductive area 34, the barrier area 36, and the firstand second electrodes 42 and 44 will be described in detail withreference to FIGS. 1 and 2.

Referring to FIGS. 1 and 2, in the present embodiment, the firstconductive area 32 and the second conductive area 34 are elongated toform stripes and are alternately arranged in the direction crossing thelongitudinal direction. The barrier area 36 may be located, as a spacer,between the first conductive area 32 and the second conductive area 34.Although not illustrated in FIGS. 1 and 2, a plurality of firstconductive areas 32, which are spaced apart from one another, may beconnected to one another at one edge, and a plurality of secondconductive areas 34, which are spaced apart from one another, may beconnected to one another at an opposite edge. However, the embodiment ofthe present invention is not limited thereto.

At this time, the first conductive area 32 may be wider than the secondconductive area 34. In one example, the areas of the first conductivearea 32 and the second conductive area 34 may be adjusted by providingthe first and second conductive areas 32 and 34 with different widths.That is, the width W1 of the first conductive area 32 may be greaterthan the width W2 of the second conductive area 34.

In addition, the first electrode 42 may have a stripe shape so as tocorrespond to the first conductive area 32, and the second electrode 44may have a stripe shape so as to correspond to the second conductivearea 34. Various other alterations are possible. In addition, althoughnot illustrated in FIGS. 1 and 2, a plurality of first electrodes 42 maybe connected to one another at one edge, and a plurality of secondelectrodes 44 may be connected to one another at an opposite edge.However, the embodiment of the present invention is not limited thereto.

Referring again to FIG. 1, the front passivation film 24 and/or theanti-reflection film 26 may be disposed over the front surface of thesemiconductor substrate 10 (for example, over the front field area 130formed on the front surface of the semiconductor substrate 10). In someembodiments, only the front passivation film 24 may be formed over thesemiconductor substrate 10, only the anti-reflection film 26 may beformed over the semiconductor substrate 10, or the front passivationfilm 24 and the anti-reflection film 26 may be disposed in sequence overthe semiconductor substrate 10. FIG. 1 illustrates that the frontpassivation film 24 and the anti-reflection film 26 are formed insequence over the semiconductor substrate 10 such that the semiconductorsubstrate 10 comes into contact with the front passivation film 24.However, the embodiment of the present invention is not limited theretoand the semiconductor substrate 10 may come into contact with theanti-reflection film 26. Various other alterations are possible.

The front passivation film 24 and the anti-reflection film 26 may beformed substantially on the entire front surface of the semiconductorsubstrate 10. Here, the expression “the film formed on the entiresubstrate” includes not only the instance where the film is physicallycompletely formed on the entire substrate, but also the instance wherethe film is inevitably formed on all except for a small portion of thesubstrate.

The front passivation film 24 comes into contact with the front surfaceof the semiconductor substrate 10 for passivation of defects present inthe front surface or the bulk of the semiconductor substrate 10. Assuch, it is possible to increase the open-circuit voltage of the solarcell 100 by removing recombination sites of minority carriers. Theanti-reflection film 26 reduces the reflectance of light introduced intothe front surface of the semiconductor substrate 10. This may increasethe quantity of light, which reaches the pn junction formed at theinterface of the base area 110 and the first conductive area 32.Thereby, the short-circuit current Isc of the solar cell 100 may beincreased. In conclusion, the front passivation film 24 and theanti-reflection film 26 may increase the open-circuit voltage and theshort-circuit current of the solar cell 100, thereby improving theefficiency of the solar cell 100.

The front passivation film 24 and/or the anti-reflection film 26 may beformed of various materials. In one example, the front passivation film24 and/or the anti-reflection film 26 may be a single-layered film or amulti-layered film having the form of a combination of two or morelayers selected from among the group of a silicon nitride layer, asilicon nitride layer containing hydrogen, a silicon oxide layer, asilicon oxide nitride layer, an aluminum oxide layer, a silicon carbidelayer, MgF₂, ZnS, TiO₂ and CeO₂. In one example, the front passivationfilm 24 may take the form of a silicon oxide layer formed on thesemiconductor substrate 10, and the anti-reflection film 26 may take theform of a stack in which a silicon nitride layer and a silicon carbidelayer are stacked one above another in sequence.

When light is introduced into the solar cell 100 in accordance with thepresent embodiment, holes and electrons are generated via photoelectricconversion at the pn junction formed between the base area 110 and thefirst conductive area 32. The generated holes and electrons move to thefirst conductive area 32 and the second conductive area 34 by passingthrough the control passivation layer 20, and thereafter move to thefirst and second electrodes 42 and 44. This results in the generation ofelectricity.

In the back contact type solar cell 100 in accordance with the presentembodiment in which the electrodes 42 and 44 are formed on the backsurface of the semiconductor substrate 10 and no electrodes are formedon the front surface of the semiconductor substrate 10, it is possibleto minimize shading loss on the front surface of the semiconductorsubstrate 10. This may improve the efficiency of the solar cell 100.However, the embodiment of the present invention is not limited thereto.

In the present embodiment, the control passivation layer 20, which is aprotective film disposed over the semiconductor substrate 10, is formedso as to have good quality. This will be described below in detail withregard to a method of manufacturing the solar cell 100 in accordancewith one embodiment of the present invention with reference to FIGS. 3Ato 3F. A detailed description related to the elements described abovewill be omitted, and only elements not described above will be describedbelow in detail.

FIGS. 3A to 3F are sectional views illustrating a method ofmanufacturing the solar cell in accordance with one embodiment of thepresent invention.

First, as illustrated by example in FIG. 3A, the control passivationlayer 20, which is a protective film, is formed over the back surface ofthe semiconductor substrate 10, which includes the base area 110containing a second conductive dopant. In the present embodiment, thecontrol passivation layer 20 is formed via a method including a heattreatment process, which is performed at a relatively high temperatureunder an atmosphere including halogen gas, which has a halogen element.

This will be described below in more detail with reference to FIGS. 4and 5 in conjunction with FIG. 3A. FIG. 4 illustrates one example of aheat treatment device, which may perform a heat treatment process in themethod of manufacturing the solar cell in accordance with one embodimentof the present invention. FIG. 5 is a view illustrating the temperaturecycle of the heat treatment process in the method of manufacturing thesolar cell in accordance with one embodiment of the present invention.

In the present embodiment, the control passivation layer 20 may beformed by arranging a plurality of semiconductor substrates 10 in a heattreatment device 200, and thereafter performing a heat treatment processon all of the semiconductor substrates 10. At this time, thesemiconductor substrates 10 may be arranged parallel to one another andspaced apart at a predetermined distance d in the heat treatment device200 so as to ensure the implementation of sufficient thermal oxidationin the heat treatment process. In one example, the distance d betweenthe semiconductor substrates 10 may be within a range from 1 mm to 5 mm.When the distance d between the semiconductor substrates 10 is below 1mm, the control passivation layer 20 may not be evenly formed due to,for example, stagnation in the flow of gas. When the distance d betweenthe semiconductor substrates 10 exceeds 5 mm, the number ofsemiconductor substrates 10 that may be processed via a single heattreatment process is not great, which may deteriorate productivity.However, the embodiment of the present invention is not limited thereto,and the distance d between the semiconductor substrates 10 may beadjusted so as to have various values.

In one example, the control passivation layer 20 may be formed via amethod including a heat treatment process, which is performed in theheat treatment device 200 at a heat treatment temperature T of 600degrees Celsius or more (for example, within a range from 600 degreesCelsius to 900 degrees Celsius) under an atmosphere including halogengas and source gas. Here, the heat treatment temperature may mean atemperature that is continuously maintained for a given time in order toform the control passivation layer 20 after the semiconductor substrate10 is introduced into the heat treatment device 200. In addition, theintroduction temperature T1 when the semiconductor substrate 10 isintroduced into the heat treatment device 200 and the dischargetemperature T2 when the semiconductor substrate 10, on which the controlpassivation layer 20 has been formed, is discharged from the heattreatment device 200 may differ from the heat treatment temperature T.Also, reference to a halogen gas also includes one or more gases in thehalogen group.

For example, the semiconductor substrate 10 is introduced into the heattreatment device 200 at the introduction temperature T1, and an increasein temperature from the introduction temperature T1 to the heattreatment temperature T occurs during a temperature increase section S1.Then, heat treatment is performed at the heat treatment temperature Tduring a main section S2. Then, a reduction in temperature from the heattreatment temperature T to the discharge temperature T2 occurs during atemperature reduction section S3, and the semiconductor substrate 10 isdischarged from the heat treatment device 200 at the dischargetemperature T2. As described above, when the introduction temperature T1and the discharge temperature T2 are lower than the heat treatmenttemperature T, deterioration in the quality of the semiconductor layer10 and the control passivation layer 20 attributable to rapid variationin temperature may be prevented or reduced.

When the heat treatment process using halogen gas is performed at theheat treatment temperature T, which is relatively high (i.e. 600 degreesCelsius or more), during the main section S2, the purity of the controlpassivation layer 20 may be increased and the density of the controlpassivation layer 20 may be increased owing to a reduction in interfacetrap density (DIT) because the halogen gas adsorbs dopant particlesduring the heat treatment process. In this way, the quality of thecontrol passivation layer 20 formed by the heat treatment process may beimproved.

The adsorption of dopant particles in the halogen gas described abovemay be remarkable at a heat treatment temperature T of 600 degreesCelsius or more, and may not be substantially evident at a heattreatment temperature below 600 degrees Celsius. In addition, thehalogen gas may remain, rather than being decomposed, at a temperaturebelow 600 degrees Celsius, which may cause the problematic leakage oftoxic halogen gas after the heat treatment process. In addition, whenthe heat treatment temperature T exceeds 900 degrees Celsius during theformation of the control passivation layer 20, the high heat treatmenttemperature may cause several problems, such as increased facilityburden and manufacturing costs, and controlling the thickness of thecontrol passivation layer 20 may become difficult, thus causingincreased unevenness of the thickness of the control passivation layer20. At this time, the heat treatment temperature T may be 650 degreesCelsius or more in order to improve the adsorption of dopant particlesin the halogen gas and to improve process stability. In addition, theheat treatment temperature T may be 850 degrees Celsius or less, so asto reduce the burden associated with a high-temperature process.

In the present embodiment, the introduction temperature T1 may be 550degrees Celsius or less (for example, within a range from 400 degreesCelsius to 550 degrees Celsius, and for example, within a range from 500degrees Celsius to 550 degrees Celsius). When the introductiontemperature T1 is below 400 degrees Celsius, the processing time of thetemperature increase section S1 may increase, or the quality of thesemiconductor substrate 10 may be deteriorated by the rapid increase intemperature. On the other hand, when the introduction temperature T1exceeds 550 degrees Celsius, it may be difficult to control thethickness of the control passivation layer 20 because the controlpassivation layer 20 may be formed on the semiconductor substrate 10even while the semiconductor substrate 10 is introduced into the heattreatment device 200. The introduction temperature T1 may be within arange from 500 degrees Celsius to 550 degrees Celsius when furtherconsidering the processing time.

In addition, the discharge temperature T2 may be 550 degrees Celsius orless (for example, within a range from 400 degrees Celsius to 550degrees Celsius, for example, within a range from 500 degrees Celsius to550 degrees Celsius). When the discharge temperature T2 is below 400degrees Celsius, the processing time of the temperature reductionsection S3 may be increased. In addition, when the discharge temperatureT2 exceeds 550 degrees Celsius, problems, such as quality deterioration,may occur due to the great variation in temperature after thesemiconductor substrate 10 and the control passivation layer 20 aredischarged from the heat treatment device 200. The discharge temperatureT2 may be within a range from 500 degrees Celsius to 550 degrees Celsiuswhen further considering the processing time.

However, the embodiment of the present invention is not limited thereto,and the introduction temperature T1 and the discharge temperature T2 maydiffer from each other.

The halogen element included in the halogen gas used during the mainsection S2 may include at least one of fluorine, chlorine, bromine,iodine, astatine, and ununseptium. This is because halogen elements havegood ability to adsorb dopant in the process of forming the controlpassivation layer 20, as described above. In particular, the halogen gasmay include chlorine as the halogen element. The halogen gas includingchlorine is readily available and exhibits considerably excellentreactive power and relatively high safety in use, and various equipmentcapable of using halogen gas has been developed. In one example, halogengas including chlorine may include at least one of Cl₂, C₂H₂Cl₂, andHCl, and more particularly, may include at least one of Cl₂ and C₂H₂Cl₂.On the other hand, halogen gas including fluorine may have an etchingproperty, and thus the use thereof may be limited. In addition, halogengas including bromine, iodine, astatine, or ununseptium may be difficultto purchase, and iodine, astatine and ununseptium entail the risk ofemitting radioactivity under specific conditions.

At this time, the quantity of halogen gas may be equal to or less thanthe quantity of oxygen gas because halogen gas may increase the growthrate of the control passivation layer 20. In one example, the volumeratio of oxygen gas to halogen gas may be within a range from 1:0.01 to1:1. When the ratio is below 1:0.01, the improvement in purityattributable to chlorine gas may be not sufficient. When the ratioexceeds 1:1, a greater quantity of chlorine gas than the requiredquantity is included, which may deteriorate the purity of the controlpassivation layer 20 and increase the growth rate of the controlpassivation layer 20, thus increasing the thickness of the controlpassivation layer 20. However, the embodiment of the present inventionis not limited thereto, and various alterations are possible.

In the present embodiment, the gas atmosphere in the heat treatmentprocess may include a source gas, in addition to the halogen gas. Hence,the control passivation layer 20 may be formed via thermal oxidation inthe heat treatment process, which is performed at a high temperature.Thereby, the control passivation layer 20 may be formed only through theheat treatment process without an additional process, which may simplifythe overall manufacturing process. In the present embodiment, the sourcegas may include oxygen gas such that the control passivation layer 20 isan oxide layer. That is, the control passivation layer 20 may be athermal oxide layer (e.g. a thermal silicon oxide layer), which isformed via the reaction of oxygen and a semiconductor material (e.g.silicon) of the semiconductor substrate 10 at a high temperature.

In addition, the gas atmosphere in the heat treatment process mayinclude various kinds of gas, in addition to oxygen gas, which is thesource gas. For example, the gas atmosphere may further include nitrogengas. Nitrogen gas is involved in the adjustment of the growth rate ofthe control passivation layer 20 and is also involved in the adjustmentof the uniformity of the control passivation layer 20, which isassociated with a leakage current and dopant penetration. The quantityof nitrogen gas may be adjusted in consideration of the size of achamber in which the control passivation layer 20 is formed. The totalquantity of halogen gas, oxygen gas and nitrogen gas may be adjusted soas to achieve a required pressure.

In the present embodiment, the heat treatment device 200, which performsthe heat treatment process, may be a typical heat treatment furnace, thepressure of which is difficult to adjust, may be a chemical vapordeposition (CVD) device, or may be a low-pressure chemical vapordeposition (LPCVD) device that may have a pressure adjustment function,and thus may perform the heat treatment process at a lower pressure thana normal pressure.

When the control passivation layer 20, which is a protective film, isformed via thermal oxidation by performing the heat treatment process inthe typical heat treatment furnace, the control passivation layer 20 maybe easily grown within a short time, which may reduce the processingtime.

A CVD device or an LPCVD device may be suitable for maintaining desiredprocess conditions. In one example, when the control passivation layer20, which is a protective film, is formed via deposition by performingthe heat treatment process in the LPCVD device, the heat treatmentprocess may be performed at a pressure lower than the normal pressure,which enables the thickness of the control passivation layer 20 to beeasily adjusted. Thereby, the control passivation layer 20 may be evenlyformed. Here, the pressure may mean the pressure of all gases includingthe source gas and other gases, i.e. the pressure in the manufacturedevice of the control passivation layer 20.

At this time, even when the CVD device or the LPCVD device is used, thesource gas does not include all source materials constituting thecontrol passivation layer 20, but includes only oxygen gas among oxidesconstituting the control passivation layer 20. That is, the source gasdoes not include the other source materials. For example, when thecontrol passivation layer 20 is a silicon oxide layer, the source gasincludes only oxygen gas, and does not include any other gas includingsilicon that is a source material. Thereby, the control passivationlayer 20 is formed via thermal oxidation in which oxygen of the oxygengas is diffused into the semiconductor substrate 10 so as to react witha semiconductor material. Unlike this, for example, in a depositionprocess, both oxygen gas including oxygen and silane (SiH₄) gasincluding silicon are supplied as a source gas. Thereby, a silicon oxideis formed when oxygen and silicon, which are separated from oxygen gasand silane gas respectively via thermal decomposition, chemically reactwith each other.

When the control passivation layer 20 is formed via thermal oxidation atthe high temperature as described above, the thickness of the controlpassivation layer 20 may be easily increased. When the controlpassivation layer 20 is formed at a pressure that is equal to or lessthan atmospheric pressure in the CVD device or the LPCVD device, a rapidincrease in the thickness of the control passivation layer 20 may beprevented or reduced (i.e. the growth rate of the control passivationlayer 20 may be controlled), which may allow the entire controlpassivation layer 20 to be evenly and thinly formed.

At this time, when the pressure in the heat treatment device 200 ismaintained at 760 Torr or less (i.e. the pressure equal to or less thanthe atmospheric pressure), even if the control passivation layer 20 isformed via thermal oxidation at the relatively high temperature, thegrowth rate of the control passivation layer 20 may be maintained at agiven level owing to the low pressure. In this way, the thickness of thecontrol passivation layer 20 may be considerably reduced.

For example, the pressure may be within a range from 1 Torr to 760 Torr(for example, within a range from 100 Torr to 760 Torr). When thepressure at which the control passivation layer 20 is formed is below 1Torr, for example, great cost is required to maintain the pressure and astrain may be imposed on the manufacture device of the controlpassivation layer 20. Giving greater consideration to the growth rate,cost, and the like, the pressure at which the control passivation layer20 is formed may be within a range from 1 Torr to 700 Torr, and moreparticularly, within a range from 1 Torr to 600 Torr, for example,within a range from 100 Torr to 600 Torr. However, the embodiment of thepresent invention is not limited thereto, and the pressure at which thecontrol passivation layer 20 is formed may be changed.

On the other hand, for example, the existing semiconductor field doesnot require a thin oxide layer, which ensures the passage of carriers,like the control passivation layer of the solar cell. That is, in thesemiconductor field, the thickness of an oxide layer is adjusted withinthe range in which carriers do not pass through the oxide layer, but itis not necessary to form the oxide layer to a thickness through whichcarriers pass. In addition, because, for example, the purity of thecontrol passivation layer has no great effect on the properties ofsemiconductor elements or the like, it has been difficult to propose amethod of increasing the purity of the control passivation layer.

However, as described above, in the present embodiment, for example, thepurity, density and thickness of the control passivation layer 20 may beadjusted when the control passivation layer 20 is formed via a methodincluding a heat treatment process, which is performed at a high heattreatment temperature T under a gas atmosphere including halogen gas(more particularly, thermal oxidation performed during the heattreatment process).

At this time, when thermal oxidation is performed at or below theatmospheric pressure in the CVD device or the LPCVD device, the growthrate of the control passivation layer 20 may be adjusted, thus enablingthe formation of a thin and even control passivation layer 20. Inaddition, in some embodiments, because a semiconductor layer (seereference numeral 300 in FIG. 3B), which is formed over the controlpassivation layer 20, is formed by a deposition equipment, when thecontrol passivation layer 20 is formed in the deposition equipment, thecontrol passivation layer 20 and the semiconductor layer 300 may beformed via in-situ processes, which are successively formed in the samedeposition equipment (e.g. the LPCVD device). When the controlpassivation layer 20 and the semiconductor layer 300 are formed via thein-situ processes as described above, the manufacturing process may besignificantly simplified, which may significantly reduce, for example,manufacturing costs and manufacturing time.

The interior temperature of the deposition equipment may be adjusted byapplying heat or removing heat for a long time and a long time isrequired to stabilize the temperature. On the other hand, the gasatmosphere and the pressure may be adjusted by varying, for example, thekind and quantity of gas to be supplied into the deposition equipment.Accordingly, the gas atmosphere and the pressure may be more easilycontrolled than the temperature.

In consideration of this, in the present embodiment, the differencebetween the temperature at which the control passivation layer 20 isformed and the temperature at which the semiconductor layer 300 isdeposited may be within 200 degrees Celsius (i.e. within a range from 0degrees Celsius to 200 degrees Celsius). For example, the differencebetween the temperature at which the control passivation layer 20 isformed and the temperature at which the semiconductor layer 300 isdeposited may be within 100 degrees Celsius (i.e. within a range from 0degrees Celsius to 100 degrees Celsius). This is because the controlpassivation layer 20 is formed at or below atmospheric pressure, andtherefore, the temperature at which the control passivation layer 20 isformed may be increased so as to reduce the difference from thetemperature at which the semiconductor layer 300 is deposited. Owing tothe fact that the temperature, which is relatively difficult to adjust,may be maintained without large change as described above, theefficiency of the in-situ processes in which the control passivationlayer 20 and the semiconductor layer 300 are successively formed may befurther increased. On the other hand, the gas atmosphere under which thesemiconductor layer 300 is deposited may differ from the gas atmosphereunder which the control passivation layer 20 is formed, and the pressureat which the semiconductor layer 300 is deposited may be the same as ordifferent from the pressure at which the control passivation layer 20 isformed.

However, the embodiment of the present invention is not limited thereto,and the control passivation layer 20 and the semiconductor layer 300 maybe formed via, for example, separate processes and devices.

Although the drawings illustrate that the control passivation layer 20is formed only on the back surface of the semiconductor substrate 10,the embodiment of the present invention is not limited thereto. Thecontrol passivation layer 20 may be additionally formed on the frontsurface and/or the side surface of the semiconductor substrate 10depending on the manufacturing method of the control passivation layer20. The control passivation layer 20, which is formed on, for example,the front surface of the semiconductor substrate 10, may be removedlater in a separate operation.

In addition, although the temperature cycle of FIG. 5 illustrates theinstance where the heat treatment process of forming the protective filmis performed alone, the embodiment of the present invention is notlimited thereto. Accordingly, as mentioned above, after the controlpassivation layer 20, which is a protective film, is formed, the controlpassivation layer 20 may be subjected to any subsequent process (e.g. aprocess of forming the semiconductor layer 300) without being dischargedfrom the heat treatment device 200. In this instance, the temperaturereduction section S3 may not be performed depending on the temperatureof the subsequent process. Alternatively, the heat treatment process maybe successively performed in a device in which a preceding processbefore the formation of the protective film has been performed. In thisinstance, the temperature increase section S1 may not be performeddepending on the temperature at which the preceding process isperformed.

Subsequently, as illustrated in FIGS. 3B to 3D, the semiconductor layer30, which includes the first and second conductive areas 32 and 34, maybe formed on the control passivation layer 20, and the texture and thefront field area 130 may be formed on the front surface of thesemiconductor substrate 10. This will be described below in more detail.

First, as illustrated by example in FIG. 3B, the semiconductor layer300, which has a crystalline structure and is formed of an intrinsicsemiconductor, is formed over the control passivation layer 20, which isformed over the back surface of the semiconductor substrate 10. Thesemiconductor layer 300 may be formed of a microcrystalline, amorphous,or polycrystalline semiconductor. The semiconductor layer 300 may beformed via, for example, thermal growth or chemical deposition (e.g.plasma chemical vapor deposition or low-pressure chemical vapordeposition). However, the embodiment of the present invention is notlimited thereto, and the semiconductor layer 300 may be formed via anyof various methods.

In one example, in the present embodiment, the intrinsic semiconductorlayer 300 may be formed by chemical vapor deposition, and moreparticularly, may be formed via low-pressure chemical vapor deposition.Accordingly, as described above, the control passivation layer 20 andthe intrinsic semiconductor layer 300 may be formed via the in-situprocesses. However, the embodiment of the present invention is notlimited thereto, and in-situ processes may not be applied to the controlpassivation layer 20 and the semiconductor layer 300.

The gas used in the process of depositing the semiconductor layer 300may include a gas (e.g. silane gas) that includes a semiconductormaterial constituting the semiconductor layer 300. In the presentembodiment, because the intrinsic semiconductor layer 300 is deposited,a gas atmosphere may be composed only of the gas including asemiconductor material. This may simplify the supply of the gas and mayincrease the purity of the semiconductor layer 300 to be formed.However, the embodiment of the present invention is not limited thereto,and any other gas may be additionally used in order to facilitate thedeposition of the semiconductor layer 300 or to improve the propertiesof the semiconductor layer 300. In addition, in the instance wheredoping using first dopant and/or second dopant is performed in theprocess of depositing the semiconductor layer 300, a gas including thefirst or second conductive dopant (e.g. B2H6 or PH3) may be additionallyused.

In addition to the gas including the semiconductor material, in theprocess of depositing the semiconductor layer 300, nitrogen dioxide(N₂O) gas and/or oxygen (O₂) gas are introduced in order to adjust, forexample, the size of crystal grains and crystallinity.

The temperature at which the semiconductor layer 300 is deposited may beequal to or less than the temperature at which the control passivationlayer 20 is formed. In particular, when the temperature at which thesemiconductor layer 300 is deposited is less than the temperature atwhich the control passivation layer 20 is formed, the semiconductorlayer 300, which is directly involved in photoelectric conversion, mayachieve uniform properties. Alternatively, the temperature at which thesemiconductor layer 300 is deposited may be within a range from 500degrees Celsius to 700 degrees Celsius. This is limited to a temperaturesuitable for the deposition of the semiconductor layer 300, which has adifferent crystalline structure from that of the semiconductor substrate10. In particular, in the instance where the semiconductor layer 300 isnot doped as in the present embodiment, the temperature at which thesemiconductor layer 300 is deposited may be within a range from 600degrees Celsius to 700 degrees Celsius because the semiconductor layer300 has a lower reaction rate than a doped semiconductor layer. In thisway, it is possible to further reduce the difference between thetemperature at which the semiconductor layer 300 is deposited and thetemperature at which the control passivation layer 20 is formed.

As described above, because the temperature at which the controlpassivation layer 20 is formed is the same as or similar to thetemperature at which the semiconductor layer 300 is deposited, forexample, the time required to adjust the temperature or the timerequired to stabilize the temperature is not required, which maysimplify the process.

Although FIG. 3B illustrates that the semiconductor layer 300 is formedonly on the back surface of the semiconductor substrate 10, theembodiment of the present invention is not limited thereto. Thesemiconductor layer 300 may be additionally formed on the front surfaceand/or the side surface of the semiconductor substrate 10 according tothe manufacturing method of the semiconductor layer 300. Thesemiconductor layer 300 formed on, for example, the front surface of thesemiconductor substrate 10 will be removed later in a separateoperation.

Subsequently, as illustrated by example in FIGS. 3C and 3D, the frontsurface of the semiconductor substrate 10 may be subjected to texturingso that protrusions are formed on the front surface of the semiconductorsubstrate 10, and the first and second conductive areas 32 and 34 andthe front field area 130 may be formed.

In one example, as illustrated by example in FIG. 3C, a portion of thesemiconductor layer 300 may be doped with a first conductive dopant soas to form the first conductive area 32 and then, as illustrated byexample in FIG. 3D, the front surface of the semiconductor substrate 10is subjected to texturing and the front surface of the semiconductorsubstrate 10 and another portion of the semiconductor layer 300 may bedoped with a second conductive dopant so as to form the front field area130 and the second conductive area 34. At this time, an undoped area,which is not doped with a dopant, may be located between the firstconductive area 32 and the second conductive area 34, and this area maybe the barrier area 36.

Various known methods may be used in the doping process of forming thefirst and second conductive areas 32 and 34 and the front field area130. In one example, various methods, such as ion implantation, thermaldiffusion, which is heat treatment using gas including a dopant, heattreatment performed after the formation of a doped layer, or laserdoping, may be applied. The embodiment of the present invention is notlimited thereto.

The texturing performed on the surface of the semiconductor substrate 10may be wet or dry texturing. Wet texturing may be performed by dippingthe semiconductor substrate 10 into a texturing solution, and has theadvantage of a short processing time. Dry texturing is the process ofgrinding the surface of the semiconductor substrate 10 using, forexample, a diamond grill or laser, and may entail the disadvantages of along processing time and the potential for damage to the semiconductorsubstrate 10, although it may be advantageous in that protrusions areformed evenly. In addition, the texturing on the semiconductor substrate10 may be, for example, Reactive Ion Etching (RIE). As such, in thepresent invention, the semiconductor substrate 10 may be subjected totexturing via various methods.

The present embodiment illustrates that, after the semiconductor layer300 and the first conductive area 32 formed in sequence, the frontsurface of the semiconductor substrate 10 is subjected to texturing,after which the front field area 130 and the second conductive area 34are formed in the same doping process. However, the embodiment of thepresent invention is not limited thereto. Accordingly, the sequence offorming the first conductive area 32, the second conductive area 34, thefront field area 130, and the texture may be altered in various ways. Inaddition, the second conductive area 34 and the front field area 130 maybe formed via different doping processes.

Subsequently, as illustrated by example in FIG. 3E, other protectivefilms are formed on the front surface and the back surface of thesemiconductor substrate 10. That is, the front passivation film 24 andthe anti-reflection film 26 are formed on the front surface of thesemiconductor substrate 10, and the back passivation film 40 is formedon the back surface of the semiconductor substrate 10.

For example, the front passivation film 24 and the anti-reflection film26 are formed over the entire front surface of the semiconductorsubstrate 10, and the back passivation film 40 is formed over the entireback surface of the semiconductor substrate 10. The front passivationfilm 24, the anti-reflection film 26, or the back passivation film 40may be formed via any of various methods such as, for example, vacuumdeposition, chemical vapor deposition, spin coating, screen printing, orspray coating. The sequence of forming the front passivation film 24,the anti-reflection film 26, and the back passivation film 40 is notlimited.

Subsequently, as illustrated by example in FIG. 3F, the first and secondelectrodes 42 and 44, which are connected respectively to the first andsecond conductive areas 32 and 34, are formed.

In one example, the first and second openings 402 and 404 are formed inthe back passivation film 40 via a patterning process, and thereafter,are filled with the first and second electrodes 42 and 44. At this time,the first and second openings 402 and 404 may be formed via any ofvarious methods, such as laser ablation using a laser, or etching usingan etching solution or etching paste. In addition, the first and secondelectrodes 42 and 44 may be formed via any of various methods, such asplating or deposition.

In another example, after a paste for the formation of the first andsecond electrodes 42 and 44 may be applied on the back passivation film40 via screen printing or the like, for example, fire-through phenomenonor laser firing contact may be used in order to form the first andsecond electrodes 42 and 44 having the above-described shape. In thisinstance, because the first and second openings 402 and 404 are formedwhen the first and second electrodes 42 and 44 are formed, no process offorming the first and second openings 402 and 404 is added.

In the present embodiment, the control passivation layer 20 may beformed via a heat treatment process, which is performed at a heattreatment temperature within a range from 600 degrees Celsius to 900degrees Celsius under a gas atmosphere including halogen gas, which mayincrease the purity and density of the control passivation layer 20 andreduce the interface trap density. Thereby, the passivation of thecontrol passivation layer 20 may be improved, and the efficiency of thesolar cell 100 may be increased owing to the smooth passage of carriers.In addition, the control passivation layer 20 may continuously maintaingood quality and properties during a subsequent high-temperatureprocess. This may further increase the efficiency of the solar cell 100because the temperature of a subsequent high-temperature process (e.g. adoping process) may be freely selected. In some embodiments, in theinstance where the control passivation layer 20 is formed at atemperature similar to the temperature at which the semiconductor layer300 will be deposited after the formation of the control passivationlayer 20, the control passivation layer 20 and the semiconductor layer30 may be formed in successive processes, which may simplify themanufacturing process.

An alternative embodiment of the method of manufacturing the solar cell100 in accordance with one embodiment described above will be describedbelow with reference to FIGS. 6A and 6B. A detailed description relatedto parts that are the same or similar to those of the embodiments withreference to FIGS. 3A to 3F and FIGS. 4 and 5 will be omitted below andthe following description will be focused on description of parts thatare different. In addition, combinations of the above-describedembodiment or alterations thereof with the following embodiment oralterations thereof fall within the scope of the present invention.

FIGS. 6A and 6B are sectional views illustrating an operation of formingthe control passivation layer in the method of manufacturing the solarcell in accordance with an alternative embodiment of the presentinvention.

Referring to FIGS. 6A and 6B, in the present alternative embodiment, thecontrol passivation layer 20, which is a protective film formed over thesemiconductor substrate 10, may be a protective film formed byperforming a heat treatment process after a preliminary protective film200 is formed.

That is, as illustrated by example in FIG. 6A, the preliminaryprotective film 200 is formed over the semiconductor substrate 10. Thepreliminary protective film 200 may be formed using any of variousprocesses, which is performed at a temperature equal to or less than thetemperature of the heat treatment process (i.e. a temperature of 600degrees Celsius or less). When the preliminary protective film 200 isformed at a lower temperature than the heat treatment process, it ispossible to prevent the addition of any high-temperature process, whichmay reduce a process burden.

In one example, the preliminary protective film 200 may be formed via awet chemical process using a wet chemical solution. In the wet chemicalprocess, the preliminary protective film 200, which has a smallerthickness and/or lower density than those of the control passivationlayer 20, is formed on the surface of the semiconductor substrate 10 viathe application or positioning of the wet chemical solution. The wetchemical solution may be any of various solutions that may be used toform the preliminary protective film 200 on the surface of thesemiconductor substrate 10 via reaction with the semiconductor substrate10. In one example, the wet chemical solution may be hydrochloric acid(HCl), hydrogen peroxide (H₂O₂), or mixtures thereof. This is becausethe solution may easily form the preliminary protective film 20, whichis formed of an oxide, on the semiconductor substrate 10 via reactionwith the semiconductor substrate 10.

Alternatively, the preliminary protective film 200 may be formed via,for example, a dry process (e.g. deposition (such as chemical vapordeposition or low-pressure chemical vapor deposition)).

Subsequently, as illustrated by example in FIG. 6B, the controlpassivation layer 20 is formed by performing a heat treatment process onthe preliminary protective film 200. Because the heat treatment processis the same as or extremely similar to the heat treatment process thatwas described above with reference to FIGS. 3A, 4 and 5, the descriptionwith reference to FIGS. 3A, 4 and 5 may be applied without change.However, the heat treatment process with reference to FIG. 6B may notrequire oxygen gas, unlike the heat treatment process described withreference to FIG. 3A, and heat treatment may be performed in the statein which oxygen gas is not provided.

As described above, in the present alternative embodiment, after thepreliminary protective film 200, which has a smaller thickness and/orlower density than the control passivation layer 20, is first formed,the control passivation layer 20 is formed via the implementation of aheat treatment process. Thereby, the uniformity and density of thepassivation control layer 20 may be increased. In addition, rather thanadditionally performing a process of forming the preliminary protectivefilm 200 illustrated in FIG. 6A, the preliminary protective film 200illustrated in FIG. 6A may be formed in a process of washing thesemiconductor substrate 10. Thereby, the preliminary protective film 200illustrated in FIG. 6A may be formed in a simplified manner without anadditional process.

The above description and the drawings illustrate that the controlpassivation layer 20 is formed via the implementation of the heattreatment process after the oxide film 200 is formed. Alternatively, theheat treatment process illustrated in FIG. 6B may be replaced withanother heat treatment process for the manufacture of the solar cell 100(e.g. the process of forming the semiconductor layer 300 illustrated inFIG. 3B, the doping process illustrated in FIG. 3D or an activation heattreatment process for the same, or the electrode forming process).However, the embodiment of the present invention is not limited thereto.

The above-described embodiment illustrates that, when the first andsecond conductive areas 32 and 34 are separately arranged over the backsurface of the semiconductor substrate 10, the control passivation layer20, which is a protective film formed over the semiconductor substrate10, is formed via the above-described heat treatment process. However,the embodiment of the present invention is not limited thereto. In oneexample, at least one of the front passivation film 24 formed over thesemiconductor layer 10 and the back passivation film 40 formed over thesemiconductor layer 30 (or the conductive areas 32 and 34) may be aprotective film formed via the above-described heat treatment process.In addition, another example of the protective film formed via theabove-described heat treatment process will be described below in detailwith reference to FIGS. 7 and 8. A detailed description related to partsthat are the same or similar to those of the embodiments with referenceto FIGS. 3A to 3F and FIGS. 4 and 5 will be omitted below and thefollowing description will be focused on description of parts that aredifferent. In addition, combinations of the above-described embodimentor alterations thereof with the following embodiment or alterationsthereof fall within the scope of the present invention.

FIG. 7 is a sectional view illustrating another example of the solarcell manufactured by the method of manufacturing the solar cell inaccordance with an embodiment of the present invention. FIG. 8 is aschematic plan view of the solar cell illustrated in FIG. 7.

Referring to FIG. 7, the solar cell 100 in accordance with the presentembodiment includes the semiconductor substrate 10 including the basearea 110, the conductive areas 32 and 34 formed on the semiconductorsubstrate 10, the front and back passivation films 24 and 40, which areprotective films formed over the semiconductor substrate 10, and theelectrodes 42 and 44, which penetrate the back passivation film 40 tothereby be connected to the conductive areas 32 and 34. At this time, atleast one of the front and back passivation films 24 and 40, which areprotective films formed over the semiconductor substrate 10, may beformed by a manufacturing method including the heat treatment process inaccordance with the present embodiment.

For example, the conductive areas 32 and 34 may include the firstconductive area 32, which is located on the front surface of thesemiconductor substrate 10 and exhibits a first conductive type, and thesecond conductive area 34, which is located on the back surface of thesemiconductor substrate 10 and exhibits a second conductive type. Inaddition, the electrodes 42 and 44 may include the first electrode 42connected to the first conductive area 32 and the second electrode 44connected to the second conductive area 34. In addition, protectivefilms formed over the semiconductor substrate 10 may include the frontpassivation film 24, which is formed on the front surface of thesemiconductor substrate 10 over the first conductive area 32, and theback passivation film 40, which is formed on the back surface of thesemiconductor substrate 10 over the second conductive area 34. Inaddition, the protective films may further include the anti-reflectionfilm 26 disposed on the front passivation film 24.

In the present embodiment, the conductive areas 32 and 34 are dopedareas, which constitute a portion of the semiconductor substrate 10, thedoped areas being formed by doping some inner areas of the semiconductorsubstrate 10 with dopants. The base area 110 and the conductive areas 32and 34, which constitute the semiconductor substrate 10 as describedabove, may be defined based on the kinds and concentrations of dopantsincluded therein. For example, an area of the semiconductor substrate 10that includes a first conductive dopant and thus exhibits a firstconductive type may be defined as the first conductive area 32, an areaof the semiconductor substrate 10 that is doped with a second conductivedopant at a low doping concentration and thus exhibits a secondconductive type may be defined as the base area 110, and an area of thesemiconductor substrate 10 that is doped with the second conductivedopant at a higher doping concentration than that in the base area 110and thus exhibits the second conductive type may be defined as thesecond conductive area 34. That is, the base area 110 and the conductiveareas 32 and 34 are areas that have the crystalline structure of thesemiconductor substrate 10 but have different conductive types anddoping concentrations.

The first conductive dopant included in the first conductive area 32 maybe an n-type or p-type dopant, and the second conductive dopant includedin the base area 110 and the second conductive area 34 may be a p-typeor n-type dopant, which is contrary to the first conductive type of thefirst conductive area 32. The description of the above embodimentrelated to the p-type or n-type dopant may be applied without change.

In one example, the first conductive area 32 may be of a p-type, and thebase area 110 and the second conductive area 34 may be of an n-type.When light is emitted to the pn junction formed by the first conductivearea 32 and the base area 110, electrons generated by photoelectricconversion move to the back surface of the semiconductor substrate 10 tothereby be collected by the second electrode 44, and holes move to thefront surface of the semiconductor substrate 10 to thereby be collectedby the first electrode 42. Thereby, electricity is generated. Whenholes, which move more slowly than electrons, move to the front surfaceof the semiconductor substrate 10, rather than the back surface, theconversion efficiency may be improved. However, the embodiment of thepresent invention is not limited thereto, and the base area 110 and thesecond conductive area 34 may be of a p-type, and the first conductivearea 32 may be of an n-type.

FIG. 7 illustrates that protrusions are formed, via texturing, on thefront surface and the back surface of the semiconductor substrate 10.However, the embodiment of the present invention is not limited thereto.Thus, protrusions may be formed, via texturing, on any one of the frontsurface and the back surface of the semiconductor substrate 10, or noprotrusions may be formed, via texturing, on the front surface and theback surface of the semiconductor substrate 10.

In the present embodiment, at least one of the front passivation film 24and the back passivation film 40, which are protective films formedrespectively on the front surface and the back surface of thesemiconductor substrate 10, may be a protective film formed via a methodincluding the heat treatment process in accordance with the presentembodiment. In one example, the passivation films 24 and 40, which areformed over the n-type area among the conductive areas 32 and 34, may beprotective films formed via a method including the heat treatmentprocess in accordance with the present embodiment. The protective film,formed via a method including the heat treatment process in accordancewith the present embodiment is a silicon oxide layer. This is becausethe silicon oxide layer has a fixed positive charge, and thus issuitable for passivation. However, the embodiment of the presentinvention is not limited thereto.

In one example, when the second conductive area 34 is of an n-type, theback passivation film 40, which is located on (e.g. in contact with) theback surface of the semiconductor substrate 10, may be a protective filmformed via a method including the heat treatment process in accordancewith the present embodiment. The thickness of the back passivation film40 may be within a range from 2 nm to 10 nm (e.g. within a range from 3nm to 6 nm). When the thickness of the back passivation film 40 is below2 nm, the passivation of the back passivation film 40 may be not good orsufficient. When the thickness of the back passivation film 40 exceeds10 nm, the processing time may be increased. When further consideringthe passivation and the processing time, the thickness of the backpassivation film 40 may be within a range from 3 nm to 6 nm. However,the embodiment of the present invention is not limited as to thethickness of the back passivation film 40.

In addition, the front passivation film 24 and/or the anti-reflectionfilm 26 may be formed of any of various materials described in the aboveembodiment. A description related thereto will be omitted.

However, the embodiment of the present invention is not limited thereto,and the first conductive area 32 may be of an n-type and the frontpassivation film 24 may be formed via the heat treatment process inaccordance with the present embodiment. Alternatively, the frontpassivation film 24 and/or the back passivation film 40 may be formed,via the heat treatment process in accordance with the presentembodiment, regardless of the conductive type. Various other alterationsare possible.

Referring to FIG. 8, the first and second electrodes 42 and 44 mayinclude a plurality of finger electrodes 42 a and 44 a, which are spacedapart from one another at a constant pitch. Although FIG. 8 illustratesthat the finger electrodes 42 a and 44 a are parallel to one another andare also parallel to the edge of the semiconductor substrate 10, theembodiment of the present invention is not limited thereto. In addition,the first and second electrodes 42 and 44 may include bus bar electrodes42 b and 44 b, which are formed in the direction crossing the fingerelectrodes 42 a and 44 a so as to connect the finger electrodes 42 a and44 a to one another. Only one bus bar electrode 42 b or 44 b may beprovided, or a plurality of bus bar electrodes 42 b or 44 b may bearranged at a larger pitch than the pitch of the finger electrodes 42 aand 44 a as illustrated by example in FIG. 8. At this time, although thewidth of the bus bar electrodes 42 b and 44 b may be larger than thewidth of the finger electrodes 42 a and 44 a, the embodiment of thepresent invention is not limited thereto. Accordingly, the width of thebus bar electrodes 42 b and 44 b may be equal to or less than the widthof the finger electrodes 42 a and 44 a.

When viewing the cross section, both the finger electrodes 42 a and thebus bar electrodes 42 b of the first electrode 42 may be formed so as topenetrate the front passivation film 24 and the anti-reflection film 26.That is, the first opening 402 may be formed so as to correspond to boththe finger electrodes 42 a and the bus bar electrodes 42 b of the firstelectrode 42. In addition, both the finger electrodes 44 a and the busbar electrodes 44 b of the second electrode 44 may be formed so as topenetrate the back passivation film 40. That is, the second opening 404may be formed so as to correspond to both the finger electrodes 44 a andthe bus bar electrodes 44 b of the second electrode 44. However, theembodiment of the present invention is not limited thereto. In anotherexample, the finger electrodes 42 a of the first electrode 42 may beformed so as to penetrate the front passivation film 24 and theanti-reflection film 26, and the bus bar electrodes 42 b may be formedover the front passivation film 24 and the anti-reflection film 26. Inaddition, the finger electrodes 44 a of the second electrode 44 may beformed so as to penetrate the back passivation film 40, and the bus barelectrodes 44 b may be formed over the back passivation film 40.

In the present embodiment, the first and second electrodes 42 and 44 ofthe solar cell 100 have a given pattern so that the solar cell 100 has abi-facial structure for allowing light to be introduced into the frontsurface and the back surface of the semiconductor substrate 10. Thereby,the quantity of light used in the solar cell 100 may be increased, whichmay contribute to the improvement of the efficiency of the solar cell100.

Although FIG. 8 illustrates that the first electrode 42 and the secondelectrode 44 have the same shape. However, the embodiment of the presentinvention is not limited thereto, and the widths and pitches of thefinger electrodes 42 a and the bus bar electrodes 42 b of the firstelectrode 42 may be different from the widths and pitches of the fingerelectrodes 44 a and the bus bar electrodes 44 b of the second electrode44. In addition, the first electrode 42 and the second electrode 44 mayhave different shapes, and various other alterations are possible. Forexample, the second electrode 44 may be not patterned, but may be formedover the entire back surface of the semiconductor substrate 10.

A process of manufacturing the solar cell 100 having the backpassivation film 40 in accordance with the present embodiment will bedescribed below with reference to FIGS. 9A to 9D. A detailed descriptionrelated to parts that are the same or similar to those of the embodimentwith reference to FIGS. 3A to 3F, FIGS. 4 and 5, and FIGS. 6A and 6Bwill be omitted below and the following description is focused ondescription of parts that are different.

FIGS. 9A to 9D are sectional views illustrating the method ofmanufacturing the solar cell in accordance with another embodiment ofthe present invention.

As illustrated by example in FIG. 9A, the first and second conductiveareas 32 and 34 are formed on the semiconductor substrate 10. The firstand second conductive areas 32 and 34 may be formed via any of variousmethods, such as thermal diffusion, ion implantation, or laser doping.

Subsequently, as illustrated by example in FIG. 9B, the back passivationfilm 40 is formed over the second conductive area 34. A heat treatmentprocess of forming the back passivation film 40 is the same as orextremely similar to the above description with reference to FIGS. 3A, 4and 5. However, in order to provide the back passivation film 40 with arelatively great or greater thickness, for example, the heat treatmenttemperature or the heat treatment time may be adjusted within theabove-described temperature range. That is, as described above, the heattreatment temperature may be 600 degrees Celsius or more (for example,within a range from 600 degrees Celsius to 900 degrees Celsius). In thepresent embodiment, for example, the heat treatment temperature may bewithin a range from 800 degrees Celsius to 900 degrees Celsius. This isbecause the back passivation film 40 may be slightly thicker than thecontrol passivation layer (see reference numeral 20 in FIG. 1), andtherefore it may be allowed to slightly increase the heat treatmenttemperature T. However, the embodiment of the present invention is notlimited thereto.

Subsequently, as illustrated by example in FIG. 9C, the frontpassivation film 24 and the anti-reflection film 26 are formed over thefirst conductive area 32.

Although FIGS. 9B and 9C and the description related thereto illustratethat the back passivation film 40 is formed prior to forming the frontpassivation film 24 and/or the anti-reflection film 26, the embodimentof the present invention is not limited thereto. The sequence of formingback passivation film 40, the front passivation film 24, and theanti-reflection film 26 may be altered in various ways. In addition, theback passivation film 40 and the front passivation film 24 may be formedat the same time using the above-described process, or the backpassivation film 40 and the anti-reflection film 26 may be formed at thesame time using the above-described process.

Subsequently, as illustrated by example in FIG. 9D, the second electrode44, which penetrates the back passivation film 40, and the firstelectrode 42, which penetrates the front passivation film 24 and theanti-reflection film 26, are formed.

When the back passivation film 40 is formed at a given heat treatmenttemperature under a gas atmosphere, the purity and density of the backpassivation film 40 may be increased, and the interface trap density maybe reduced. In addition, the back passivation film 40 may achieve goodstability even in a subsequent high-temperature process. Although theabove description illustrates that only the back passivation film 40 isformed at a given temperature under a gas atmosphere, the frontpassivation film 24 or the anti-reflection film 26 may also be formed atthe above-described heat treatment temperature T under a gas atmosphere.Another example of the protective film, which may be manufactured viathe above-described heat treatment process, will be described below indetail with reference to FIGS. 10A to 10D. Because the embodiment ofFIGS. 10A to 10D is the same as or similar to the embodiment describedwith reference to FIGS. 1 to 5, the description with reference to FIGS.1 to 5 may be applied without change. Thus, a detailed descriptionrelated to parts that are the same or similar to those of theembodiments with reference to FIGS. 1 to 5 will be omitted below and thefollowing description will be focused on description of parts that aredifferent. In addition, combinations of the above-described embodimentor alterations thereof with the following embodiment or alterationsthereof fall within the scope of the present invention.

FIGS. 10A to 10D are sectional views illustrating the method ofmanufacturing the solar cell in accordance with a further embodiment ofthe present invention.

The present embodiment differs from the embodiment described withreference to FIGS. 3A to 3F in terms that the back passivation film 40and/or the front passivation film 24 are formed via heat treatment undera gas atmosphere including halogen gas, although the solar cell 100 ismanufactured as illustrated by example in FIGS. 1 and 2.

As illustrated by example in FIG. 10A, the control passivation layer 20,the semiconductor layer 30 including the first and second conductiveareas 32 and 34, a texture and the front field area 130 on the frontsurface of the semiconductor substrate 10 are formed on thesemiconductor substrate 10. The control passivation layer 20 may beformed via any of known various methods, and the other forming processesmay be formed via the same method as that described above with referenceto FIGS. 3A to 3D.

Subsequently, as illustrated by example in FIG. 10B, other protectivefilms are formed on the front surface and/or the back surface of thesemiconductor substrate 10. For example, the front passivation film 24is formed on the front surface of the semiconductor substrate 10, andthe back passivation film 40 is formed on the back surface of thesemiconductor substrate 10.

In the present embodiment, the back passivation film 40 and the frontpassivation film 24 are formed via a method including a heat treatmentprocess, which is performed at a relatively high temperature under a gasatmosphere including halogen gas, which has a halogen element. The heattreatment process is the same as or extremely similar to that describedabove with reference to FIGS. 3A, 4 and 5. However, in order to providethe front and back passivation films 24 and 40 with a relatively greator greater thickness, for example, the heat treatment temperature or theheat treatment time may be adjusted within the above-describedtemperature range. That is, as described above, the heat treatmenttemperature may be 600 degrees Celsius or more (more specifically,within a range from 600 degrees Celsius to 900 degrees Celsius). In thepresent embodiment, for example, the heat treatment temperature may bewithin a range from 800 degrees Celsius to 900 degrees Celsius. This isbecause the front and back passivation films 24 and 40 may be slightlythicker than the control passivation layer (see reference numeral 20 inFIG. 1), and therefore it may be allowed to slightly increase the heattreatment temperature T. However, the embodiment of the presentinvention is not limited thereto.

In the heat treatment process of the present embodiment, the front andback passivation films 24 and 40 may be formed via thermal oxidation.The front and back passivation films 24 and 40 may be oxide layers whena source gas includes oxygen gas. In one example, the front and backpassivation films 24 and 40 may be thermal oxide (e.g. thermal siliconoxide) layers, which are formed via the reaction of oxygen and asemiconductor material (e.g. silicon) of the semiconductor substrate 10at a high temperature.

In the present embodiment, a semiconductor material, which has athickness within a range from 1 nm to 3 nm, may be combined with oxygenon the surface of the semiconductor layer 30, so as to form the frontand back passivation films 24 and 40, each of which has a thicknesswithin a range from 3 nm to 6 nm. When the front and back passivationfilms 24 and 40 have this thickness, significantly improved passivationmay be achieved. That is, when the thickness of each of the front andback passivation films 24 and 40 is below 3 nm, it may be difficult torealize sufficient passivation. When the thickness of each of the frontand back passivation films 24 and 40 exceeds 6 nm, the time of the heattreatment process is increased, thus causing deterioration in theproperties of the semiconductor layer 30. The thickness of thesemiconductor layer 300 combined with oxygen, the thickness of the frontand back passivation films 24 and 40, and the like may be measured andevaluated using, for example, a transmission electronic microscope(TEM).

At this time, when the front passivation film 24, which is located closeto the front surface of the semiconductor substrate 10, is formed viathe above-described heat treatment process, the front passivation film24 has good quality. Thereby, the front passivation film 24 may achievesignificantly improved passivation. At this time, because the inside(bulk) of the semiconductor substrate 10 is exposed by the texture onthe front surface of the semiconductor substrate 10, a greater amount ofions (e.g. sodium ions), which cause deterioration in quality, arepresent on the front surface than on the back surface, and thusso-called gettering effects may greatly occur on the front surface. Whenthe front passivation film 24 has good quality, passivation effects maybe significantly enhanced.

In the present embodiment, the front and back passivation films 24 and40, which are located on opposite sides of the semiconductor substrate10, are formed at the same time, such that the front passivation film 24is used on the front surface without patterning, whereas the backpassivation film 40 is patterned on the back surface as illustrated byexample in FIG. 10D. This may simplify processing. However, theembodiment of the present invention is not limited thereto. The frontpassivation film 24 and the back passivation film 40 may be formed viadifferent processes, and the above-described heat treatment process maybe applied to at least one of the front passivation film 24 and the backpassivation film 40. Alternatively, after both the front passivationfilm 24 and the back passivation film 40 are formed, one of them may beremoved. Alternatively, the anti-reflection film 26 and the backpassivation film 40 may be formed at the same time via theabove-described heat treatment process. Various other alterations arepossible.

Subsequently, as illustrated by example in FIG. 10C, in the presentembodiment, the anti-reflection film 26 may be formed over the frontpassivation film 24. In one example, the anti-reflection film 26 may beformed over the entire front passivation film 24. The anti-reflectionfilm 26 may be formed via any of various methods, such as vacuumdeposition, chemical vapor deposition, spin coating, screen printing, orspray coating.

Subsequently, as illustrated by example in FIG. 10D, the first andsecond electrodes 42 and 44, which are connected respectively to thefirst and second conductive areas 32 and 34, are formed. The descriptionwith reference to FIG. 3F may be directly applied thereto, and thus, adetailed description thereof will be omitted.

Hereinafter, the present invention will be described in more detail withreference to Experimental Examples of the present invention. However,the Experimental Examples of the present invention are merely given toillustrate the present invention, and the embodiment of the presentinvention is not limited thereto.

Experimental Example 1

A solar cell having the structure illustrated in FIG. 1 wasmanufactured. At this time, a silicon oxide layer, which has a thicknessof 2 nm, was formed via thermal oxidation in a heat treatment process,which was performed at a temperature of 700 degrees Celsius under a gasatmosphere including Cl₂ gas, O₂ gas and N₂ gas. The formed siliconoxide layer was included as a control passivation layer. In the heattreatment process, the ratio of O₂ gas:Cl₂ gas was 1:0.1.

Experimental Example 2

A solar cell having the structure illustrated in FIG. 1 wasmanufactured. At this time, after a thin oxide film was formed while asemiconductor substrate was being washed with a mixture solution of HCland H₂O₂, the thin oxide film was subjected to a heat treatment process,which was performed at a temperature of 700 degrees Celsius under a gasatmosphere including Cl₂ gas, O₂ gas and N₂ gas. The formed siliconoxide layer, which has a thickness of 2 nm, was included as a controlpassivation layer. In the heat treatment process, the ratio of O₂gas:Cl₂ gas was 1:0.1.

Comparative Example 1

A solar cell was manufactured by the same method as that of ExperimentalExamples except for the process of forming a control passivation layer.At this time, a silicon oxide layer, which has a thickness of 2 nm, wasformed via thermal oxidation in a heat treatment process, which wasperformed at a temperature of 500 degrees Celsius under a gas atmosphereincluding Cl₂ gas, O₂ gas and N₂ gas. The formed silicon oxide layer wasincluded as a control passivation layer.

Comparative Example 2

A solar cell was manufactured by the same method as that of ExperimentalExamples except for the process of forming a control passivation layer.At this time, a silicon oxide layer was formed via thermal oxidation ina heat treatment process, which was performed at a temperature of 700degrees Celsius under a gas atmosphere including O₂ gas and N₂ gas. Theformed silicon oxide layer, which has a thickness of 2 nm, was includedas a control passivation layer.

Photoluminescence (PL) photographs of the solar cells in accordance withExperimental Example 1 and Comparative Examples 1 and 2 were captured.The PL photograph of the solar cell in accordance with ExperimentalExample 1 is illustrated in FIG. 11, the PL photograph of the solar cellin accordance with Comparative Example 1 is illustrated in FIG. 12, andthe PL photograph of the solar cell in accordance with ComparativeExample 2 is illustrated in FIG. 13. In the PL photographs, a brightportion is a portion in which no metal impurities, defects, and the likeare present, and a dark portion is a portion in which metal impurities,defects, and the like are present.

Referring to FIG. 11, it will be appreciated that the solar cell inaccordance with Experimental Example 1 appears bright in light ingeneral, and thus substantially no metal impurities, defects, and thelike are present. On the other hand, referring to FIG. 12, it will beappreciated that the solar cell in accordance with Comparative Example 1has a black portion, and thus metal impurities, defects, and the likeare present on the corresponding portion. In addition, referring to FIG.13, it will be appreciated that the solar cell in accordance withComparative Example 2 appears black in general, and thus manyimpurities, defects, and the like are present in the solar cell.

As described above, in Experimental Example 1 and Comparative Examples 1and 2, all other manufacturing processes are the same, and only theprocess of forming the control passivation layer is different.Accordingly, it will be appreciated that the control passivation layerhaving good properties was formed in a heat treatment process, which wasperformed at a heat treatment temperature of 600 degrees Celsius or moreunder a gas atmosphere including halogen gas. In addition, it will beappreciated that the control passivation layer having good propertieswas not formed in Comparative Example 1 in which the heat treatmentprocess was performed at a heat treatment temperature below 600 degreesCelsius even if a gas atmosphere including halogen gas is provided, andin Comparative Example 2 in which the heat treatment process wasperformed under a gas atmosphere including halogen gas even if a heattreatment temperature is 600 degrees Celsius or more.

The results of measuring implied open-circuit voltages Voc of the solarcells in accordance with Experimental Example 1 and Comparative Example1 are illustrated in FIG. 14. Referring to FIG. 14, it will beappreciated that the implied open-circuit voltage of the solar cell inaccordance with Experimental Example 1 is higher than the impliedopen-circuit voltage of the solar cell in accordance with ComparativeExample 1 by about 50 mV. The control passivation layer in accordancewith Experimental Example 1 in which the heat treatment process wasperformed at a heat treatment temperature of 600 degrees Celsius or moreunder a gas atmosphere including halogen gas has a low interface trapdensity, and thus it is expected that the solar cell including the samehas a high implied open-circuit voltage. On the other hand, the controlpassivation layer, which was formed at a heat treatment temperature of600 degrees Celsius or less as in Comparative Example 1 has a higherinterface trap density than that in Experimental Example 1, and thus itis expected that the solar cell including the same has a relatively lowimplied open-circuit voltage.

In addition, the results of measuring implied open-circuit voltages Vocof the solar cells in accordance with Experimental Examples 1 and 2 andComparative Example 1 after performing additional heat treatment at atemperature of 900 degrees Celsius are illustrated in FIG. 15. It willbe appreciated that the implied open-circuit voltages of the solar cellsin accordance with Experimental Examples 1 and 2 are higher than theimplied open-circuit voltage of the solar cell in accordance withComparative Example 1 by about 100 mV. Thereby, it will be appreciatedthat the solar cells in accordance with Experimental Examples 1 and 2have good stability even in a subsequent high-temperature process,whereas the properties of the solar cell in accordance with ComparativeExample 1 may be deteriorated in a subsequent high-temperature process.

In accordance with the embodiments of the present invention, protectivefilms including, for example, a control passivation layer and front andback passivation films are formed via a method including a heattreatment process, which is performed at a specific temperature under agas atmosphere, thereby achieving improved properties and qualities.Thereby, the efficiency of the solar cell may be improved. In addition,the formed protective films may continuously maintain good qualities andproperties in a subsequent high-temperature process, thus improvingprocess stability.

The above described features, configurations, effects, and the like areincluded in at least one of the embodiments of the present invention,and should not be limited to only one embodiment. In addition, thefeatures, configurations, effects, and the like as illustrated in eachembodiment may be implemented with regard to other embodiments as theyare combined with one another or modified by those skilled in the art.Thus, content related to these combinations and modifications should beconstrued as including in the scope and spirit of the invention asdisclosed in the accompanying claims.

What is claimed is:
 1. A method of manufacturing a solar cell, themethod comprising: forming a protective film over a semiconductorsubstrate, the semiconductor substrate including a base area of a firstconductive type and formed of crystalline silicon, wherein the formingof the protective film includes a heat treatment process performed at aheat treatment temperature of approximately 600 degrees Celsius or moreunder a gas atmosphere including nitrogen, and wherein the heattreatment process includes: a main section, during which the heattreatment temperature is maintained, a temperature increase sectionbefore the main section, during which an increase in temperature occursfrom an introduction temperature to the heat treatment temperature, anda temperature reduction section after the main section, during which adecrease in temperature occurs from the heat treatment temperature to adischarge temperature.
 2. The method according to claim 1, wherein theforming of the protective film includes at least one of the following:forming the protective film via thermal oxidation by performing the heattreatment process in a heat treatment furnace; forming the protectivefilm via deposition by performing the heat treatment process in alow-pressure chemical vapor deposition device; and forming theprotective film by performing a wet chemical process or a dry process offorming a preliminary protective film at a temperature of approximately600 degrees Celsius or less, and thereafter thermally treating thepreliminary protective film at a temperature of approximately 600degrees Celsius or more via the heat treatment process.
 3. The methodaccording to claim 1, wherein the gas atmosphere further includes oxygengas as a source gas so that the protective film includes a silicon oxidelayer.
 4. The method according to claim 1, wherein the heat treatmenttemperature of the heat treatment process is within a range fromapproximately 600 degrees Celsius to approximately 900 degrees Celsius.5. The method according to claim 1, wherein the introduction temperatureor the discharge temperature is within a range from approximately 400degrees Celsius to approximately 550 degrees Celsius.
 6. The methodaccording to claim 5, wherein the introduction temperature or thedischarge temperature is within a range from approximately 500 degreesCelsius to approximately 550 degrees Celsius.
 7. The method according toclaim 1, further comprising, before the forming of the protective film,forming a conductive area, which is one of the first conductive typehaving a higher doping concentration than that of the base area and asecond conductive type opposite to the first conductive type, by dopingan inside of the semiconductor substrate with a dopant, wherein, in theforming the protective film, the protective film is then formed over theconductive area.
 8. The method according to claim 7, wherein theprotective film has a thickness within a range from approximately 3 nmto 6 nm.
 9. The method according to claim 1, further comprising, beforethe forming of the protective film, forming a conductive area over onesurface of the semiconductor substrate, the conductive area having adifferent crystalline structure from that of the semiconductorsubstrate, wherein, in the forming of the protective film, theprotective film is then formed over the conductive area.
 10. The methodaccording to claim 9, wherein, in the forming of the conductive area, afirst conductive area, which is of the first conductive type, and asecond conductive area, which is of the second conductive type oppositeto the first conductive type, are formed in the same plane over onesurface of the semiconductor substrate, and wherein the protective filmcovers both the first conductive area and the second conductive area.11. The method according to claim 10, wherein the protective film has athickness within a range from approximately 3 nm to 6 nm.
 12. The methodaccording to claim 1, wherein, in the forming of the protective film,the protective film is a control passivation layer formed over onesurface of the semiconductor substrate, and wherein the method furthercomprises, after the forming of the protective film, forming aconductive area over the control passivation layer.
 13. The methodaccording to claim 12, wherein, in the forming the conductive area, afirst conductive area, which is of the first conductive type, and asecond conductive area, which is of a second conductive type opposite tothe first conductive type, are formed in the same plane over the controlpassivation layer.
 14. The method according to claim 12, wherein thecontrol passivation layer has a thickness within a range fromapproximately 1 nm to 2 nm.
 15. The method according to claim 1, whereinthe protective film is at least one of a first passivation film locatedover one surface of the semiconductor substrate and a second passivationfilm over a remaining surface of the semiconductor substrate.
 16. Themethod according to claim 15, wherein the first passivation film and thesecond passivation film are formed at the same time via the heattreatment process.
 17. The method according to claim 1, wherein theprotective film is an anti-reflection film.
 18. The method according toclaim 1, wherein the protective film includes at least one of silicon,carbon, oxygen and nitrogen.
 19. The method according to claim 1,wherein the introduction temperature and the discharge temperature aredifferent from each other.
 20. The method according to claim 1, whereinprocessing times of the temperature increase section and the temperaturereduction section are different from each other.